Mikaela Shiffrin, the Alpine ski racer, should win at least one gold medal at the Olympics this winter in South Korea. She might even win three. It’s a fair bet she’ll get the Wheaties box and the full-on Up Close and Personal. She’s a bright, affable American who dominates her corner of the sport with the kind of predictability and grace that draws in casual viewers, awes the experts, and inspires a lot of super-slo-mo check-that-out. There’s something about transcendent talent that causes people to root for it, no matter their allegiances or their usual embrace of the underdog. Excellence creates its own weather.

Yet so much can go wrong. For skiers, the Olympics are a brief fever dream in the middle of the five-month odyssey of their season. There are a lot of chances beforehand to get hurt. In a short race, anyone can make a ruinous mistake (lose an edge, hook a tip, choose the wrong line) or encounter bad luck (equipment malfunction, snow squall, gust of wind). And what about food poisoning? Or even geopolitics: the time would seem inopportune for an international sporting carnival on the Korean peninsula.

Athletes are taught, and sometimes even born, not to think this way. Control what you can. Eliminate distraction. Preparation is perspiration. Yet even Shiffrin, a stone-cold killer on snow, has recently found herself more susceptible to the whisperings of “what if.” “I never used to feel nervous,” she told me. “Just excited. But this past season I got so nervous I had to throw up a couple of times.” The first wave of her new anxiety came a year ago, when the International Ski Federation (F.I.S.) World Cup tour came to the Eastern United States, for the first time in a quarter of a century. The circuit typically passes over New England’s relatively diminutive mountains and variable conditions in favor of the sunny, chalky Rockies. But the Northeast has the higher concentration of racers, the deeper ski-racing history, and the more fanatical fan base. It is also, in a roundabout yet essential way, Shiffrin’s home turf. (She lives in Vail, Colorado, but her formative training years were spent on the East Coast, where her forebears are from.)

The races, held at Killington, in Vermont, over the weekend of Thanksgiving, attracted thirty thousand fans, far more than you’d ever get out West. They were there to see Shiffrin win both the slalom and the giant-slalom races. “Killington was a lot of pressure, and I didn’t realize it till I was there,” Shiffrin told me. “I was kind of freaking out.” Her extended family, including her grandmother, who was ninety-five, came to watch her race. The scrutiny brought on self-consciousness. “Instead of just answering questions, I started to hear myself answering them,” she said. She took fifth in the giant slalom, a disappointment. She won the slalom, as she almost always does, but by less than a second, which was, by her standards, a narrow margin.

A pattern was developing of Shiffrin’s dominating in training but encountering nerves and some tactical indecision on race day. Her mother, Eileen, her de facto coach, taskmaster, and wingman, suggested that she talk to a sports psychologist. Shiffrin had a couple of consultations, via Skype. “It didn’t feel like I was seeing a shrink,” she said. “It was a reminder that sometimes it’s better to be oblivious, but I’m not oblivious anymore, so how do I handle that?”

Shiffrin, who is twenty-two now, was fifteen when she first appeared on the World Cup tour—the top international tier of racing, as big in Europe, you might say, as Nascar is in America. She’d been routinely obliterating her peers in the ski-racing equivalent of the minor leagues by several seconds—a lifetime in the sprint of a ski race. (The margins are typically tenths or even hundredths of seconds.) A few weeks later, at just sixteen, she became the youngest skier ever to win a U.S. national championship. At seventeen, she started winning World Cup slalom races in bunches. (Lindsey Vonn, the greatest American skier ever, won her first race at the age of twenty.) By eighteen, Shiffrin had won a gold medal at the Sochi Olympics and become something of a household name. She has won all three slalom World Championships she has competed in and four of the past five World Cup slalom titles. (She was injured for half the season the year she didn’t win.) Last March, at the World Cup finals, in Aspen, Colorado, she also clinched the over-all title—compiling more points across all the disciplines than anyone else—the ultimate prize, in the eyes of practitioners, far greater than Olympic gold.

I first heard of Shiffrin the winter of her first World Cup race. Ski-racing people spoke of her with the same astonishment that greeted the kid-phenom incarnations of Wayne Gretzky and Tiger Woods. Once she hit the tour, I tuned in when I could, eager to see a manifestation of genius. What I saw was a skier who looked flawless and smooth but not revolutionary or enthralling. She was so good at going fast that she didn’t look fast. Technique disguised athleticism.

Did I know what to look for? I’d been admiring the top racers for years. I raced (poorly) in high school, in New Hampshire. My grandfather skied in the Olympics, in the thirties, and his sister was a slalom world champion. (Ski racing may be the only sport in which women have been competing alongside men, on a fairly equal footing, from the get-go, a century ago.) So, watching Shiffrin on TV, I’d venture remarks about her fine balance, composure, and edge control. Strong ankle pressure. But I was mostly full of it. The subtler mechanics of the ski turn are obscure, even to most people who know how to make a good one.

My presumption was that her excellence was innate. One sometimes thinks of prodigies as embodiments of peculiar genius, uncorrupted by convention, impossible to replicate or reëngineer. But this is not the case with Shiffrin. She’s as stark an example of nurture over nature, of work over talent, as anyone in the world of sports. Her parents committed early on to an incremental process, and clung stubbornly to it. And so Shiffrin became something besides a World Cup hot shot and a quadrennial idol. She became a case study. Most parents, unwittingly or not, present their way of raising kids as the best way, even when the results are mixed, as such results usually are. The Shiffrins are not shy about projecting their example onto the world, but it’s hard to argue with their findings. “The kids with raw athletic talent rarely make it,” Jeff Shiffrin, Mikaela’s father, told me. “What was it Churchill said? Kites fly higher against a headwind.”

Skiers have long been psycho about their off-season workouts. In the old days, they chopped wood, baled hay, ran up and down mountains, and rode motorcycles at a hundred miles an hour. Now they train like astronauts. Shiffrin spent this past summer in a series of training blocks, both on and off the snow—in Colorado, California, Chile, New Zealand, and Park City, Utah. I spent a few days with her in June in Park City, where the U.S. ski team and its eighty-five-thousand-square-foot training facility, the Center of Excellence, are based. Since the Winter Olympics in 2002, Park City, flush with the state-of-the-art facilities that were built for the Games, has become a hub of hale but half-broke world-class competitors in obscure frozen-water sports. When Shiffrin and I had dinner one night in town, the waiter, knowing a jock when he saw one, asked her, “What’s your sport?” Then he announced that he was on the national skeleton team.

Shiffrin was staying with her physiotherapist, Lyndsay Young, and Young’s husband, Chris, in their condo, and checking in for daily torture sessions at the Center of Excellence, under the lash of her coach, Jeff Lackie. (Young and Lackie travel with her on tour and for much of the off-season.)

June is the busiest time of year at the C.O.E. On the first morning I visited, its vast gym, girded with giant photos of past American medallists (there has been more excellence, through the decades, than one might recall or assume), slowly filled with snow-sliders of many disciplines and body types—variations on freakishly fit. When I asked Shiffrin to identify the biggest beast in the place, she pointed to Steven Nyman, a veteran American downhiller, and then said, “Or me.”

Shiffrin is lean, of medium height, with broad shoulders and, like everyone there, powerful legs. She had on black shorts and a purple tank top. You could see traces of boot-bang bruises on her shins. She began by warming up for ten minutes on a stationary bike and then doing some stretching. Eminem on the speakers, trash talk on the mats. She said that the day before had been a rough one—lifting weights, jumping up stairs.

Young said, “When Mika got home last night, she said, ‘Whoever invented stairs is the biggest asshole.’ ”

“Today is more anaerobic,” Lackie said. “You’ll have to perform consecutive days on tour, so we’re training for that.”

First up was interval training. She sprinted the length of the gym while pulling a weighted sled, then ran back while pushing a heavier sled, then did bouncy squat-like reps on a contraption that seemed to mimic skiing over bumps, then dragged a weighted sled backward, then rowed hard on an ergometer, then skated side to side in her stocking feet on a slide board while holding a ten-pound medicine ball. When Shiffrin works out, you are not supposed to cheer her on. “The motivation must come from within” is a mantra I heard her and others repeat. Still, as she did the slide board, Lackie harangued her: “Stay low, c’mon. Push, push, push, push.” He told me, “This is a skiing-like exercise at the end of the circuit to see whether she can maintain composure and form even under fatigue.” She could.

She rested for two minutes, and then did the circuit again. After the second go-round, she collapsed to the ground and crawled, like a parched man in a desert cartoon. “This is not the most flattering workout,” Lackie observed. By the end of the third circuit, as she crawled along the mat, leaving a trail of sweat, I had to look away. And this was a recovery day.

After a couple of minutes spent cooling down on the stationary bike, she could speak. “I’ve never puked,” she said. “I’ve come close. I’d pass out before I’d puke. We have a grading scale that I fill out for every workout. Ten is dying or passing out. I rate nine fairly often. That may have been a nine, maybe.” Her pulse had topped out at a hundred and sixty-six beats per minute. She’s never seen it above a hundred and eighty-five. Her resting heart rate is forty b.p.m.

Rap music had given way to hair metal. Shiffrin put in an hour of balance work. Toward the end, she walked back and forth on a slack line and picked up cones, which she put on her head or threw at Lackie. “Motivation comes from within,” she said.

Afterward, she spent half an hour on the physio table, with her legs encased in NormaTec pressure pouches, which apparently squeeze out the lactic acid, like toothpaste from a tube. On the table next to her was Joss Christensen, the 2014 slopestyle Olympic gold medallist, who’d recently torn up his knee and would likely be off snow for six months. They didn’t talk. Instead, Shiffrin tended her social-media feeds. Then she drove back to the condo, where she reheated the last of a batch of chicken strips with salsa, cheese, and rice that she’d cooked earlier in the week. Lunch. She said that she consumes about twenty-five hundred calories a day. She averages nine hours of sleep a night and is famous for her naps—she requires an hour a day, and has been known to snooze in the snow in the starting area of a race. She has only once had more than one alcoholic drink at a time and has never experienced a hangover. In her spare time, she binges on TV shows in sync with her mother (“Bones,” “Blue Bloods”) or studies German, the language of the World Cup, checking in now and then with a tutor in Denver, via Skype. “It’s a work in progress,” she said. Last fall, at an Austrian sports-awards ceremony in Vienna, she presented a trophy, in German, to the world’s best male slalom skier, Marcel Hirscher. “I made one mistake,” she said. “Athlete of the year, it was between Hirscher and Dominic Thiem, the tennis player. I said, ‘Marcel’s a great athlete, and so am I.’ ”

Shiffrin’s parents are products of New England’s mid-century ski-area boom, when you could hardly find a hill that didn’t have a rope tow or even—height of luxury—a chairlift or two. Eileen Shiffrin, née Condron, is from Lanesborough, Massachusetts, in the Berkshires. Her father was an engineer at General Electric, in neighboring Pittsfield. She learned to ski when she was three, in a dairy pasture across the street, which she and her siblings called Killer Hill. She was soon a regular at the Mount Greylock Ski Club, a private set of runs and rope tows on the northern flank of Mt. Greylock, the state’s highest peak, and the site of the Thunderbolt Trail, an early crucible for racers from all over Europe and North America. The Condrons volunteered at the club, clearing trees and brush in the fall with a sickle. Later, Eileen was a season-pass-holder and regular after-schooler and night-skier at Brodie, another hill in the area, which is now defunct. In high school, she took up racing. “I got good results, but had little formal training and didn’t take it seriously,” she said. “For me, it was totally social.”

She had to quit skiing for four years, while she got a nursing degree at the University of New Hampshire. “We weren’t allowed to do sports,” she said. But, in 1985, while working in the I.C.U. at the St. Elizabeth Hospital, outside Boston, she met Jeff Shiffrin, a resident anesthesiologist. Jeff had grown up in northern New Jersey, where his father ran a couple of liquor stores, and he had raced locally at Great Gorge, and on weekends up in Vermont, and then on the B-team at Dartmouth. He brought Eileen to Killington one weekend. He’d recently taken up Masters racing—a recreational circuit for adults. “I dragged Eileen into it,” he said.

Eileen, a meticulous and studious woman, was soon obsessed. She pored over videos of World Cup champions, read everything she could about the art of carving a turn, and mastered the methodical process of tuning skis. “I learned as much as a lot of the racers had in their ski-academy days,” she said. Before long, she was winning national and international Masters championships. Jeff liked to tell her that she could probably walk on to the national team. “Hey, she might have been an Olympic skier,” Jeff told me.

But, of course, such things aren’t possible; she’d started too late and failed to take it seriously early on. When she and Jeff had children, they wouldn’t make this mistake. Mikaela was their second child. Her brother, Taylor, is two years older. “He was the practice brother,” Jeff said. They had settled in Vail. “We had this concept that there had to be a gradual progression of skill acquisition,” Jeff said. As with Taylor, they dragged Mikaela around the living room and the driveway on skis when she was a toddler, and then taught her to cross-country ski on the golf course. Next, hard boots, skis with edges, and then follow-me. They hardly bothered with the snowplow, the customary introductory gravity-mitigation technique. The goal was a proper turn, with the skis parallel. (Kids are typically taught “pizza” before they graduate to “French fries.”) When Mikaela was in kindergarten, the teacher for the kids’ Friday skiing class, not accustomed to such small-fry French-frying, said, “I don’t have a group for her.”

“So she kept skiing with us,” Jeff said. “That became Eileen’s job.”

Eileen and Mikaela started logging the hours. After Mikaela began to ski with other kids, Eileen became their coach. She was the hands-on drillmaster, the fastidious worrywart. She was also homeschooling Mikaela. “I taught myself to do the things I was teaching the kids,” she said. “Play guitar, play piano, paint.” Whatever they took up, whether it was soccer, tennis, the unicycle, or Ping-Pong, they studied video. “We had a methodical way of doing things,” Eileen said. “Let’s see if we can simplify this chaotic life.”

When Mikaela was eight, the family moved back East, to a house in rural New Hampshire. Jeff had got a job at Dartmouth Hospital, but the kite-in-the-headwind principle factored in, too. “We thought, Maybe we have something special here,” Jeff said. “We need to see if the kids love skiing in conditions where it’s pretty easy to hate it.”

Northeastern skiing is infamous for its ice. The climate is damper and generally more miserable than in the Rockies or the Alps; cycles of thaw and freeze transform the snow surface into a rink. Recreational skiers abhor ice, but it has its virtues. A firm surface, as the understatement goes, provides a better test for élite racers and bears up better under the erosive effect of their powerful carving turns. On the World Cup circuit, in friendlier climes, course workers replicate these conditions by injecting water into the snow—with hoses, not syringes. So the Northeast’s naturally occurring “bullet” (short for “bulletproof surface”) is, and has long been, a great training and proving ground for young racers.

Mikaela Shiffrin, a budding masochist, took to this ungenerous ratio of pleasure to woe. She thrived on bullet. At the age of twelve, she began working with Kirk Dwyer, the head coach at Burke Mountain Academy, where he was also the headmaster. Burke, in northern Vermont, is a boarding school devoted to ski racing—it was the first of its kind when it was founded, in 1970. There are only about a dozen students per grade, some of whom wind up on the national team. Taylor enrolled as a boarder, but Mikaela was too young. After two good years, the family moved back to Vail, where Jeff had a new job. Mikaela was despondent. She missed her friends, her coaches, and the ice. She lost interest in her training and her studies. She began taking four-hour naps. Alarmed, Jeff and Eileen sent Mikaela back to Vermont, to train and board at Burke. Eileen and Taylor eventually followed, while Jeff stayed behind.

Mikaela arrived at Burke in December, 2009, as a freshman. One of her roommates was a racer from Connecticut called Bug Pech, the niece of the Olympian Chip Knight. (New England skiing, like medieval Scotland, can seem to be dominated by a handful of hardy clans: the Cochrans, the Shaws, the Knights.) “We were inseparable,” Pech said recently. “Piglet and Pooh Bear. She’s Piglet. She was shy, quirky. I was lost in la-la land.”

Pech had been competing with, and losing to, Shiffrin since they were eight. Now she began to see why. “It was bizarre in the most extreme way that this kid, at this place, Burke, where everyone is absolutely absorbed in ski racing, had this whole other level of devotion. Her need of ski racing is like a need for oxygen.” Pech recalled a day when it snowed several feet—a rare treat, in those hills, and by custom an excuse to blow off practice and ski for fun. “We were all ripping powder, hucking cliffs in the woods. Meanwhile, Mikaela was doing drills on her racing skis. She’d rather do drills than ski powder with her buddies.” (“Powder? There’s no room for that,” Jeff told me. “That’s for also-rans. Sorry, that’s the way it is.”)

Eileen had a condo a few minutes from the Burke campus, but she spent most of her time on the ski hill with Mikaela or in Mikaela’s triplex. “She was very much a presence,” Pech said. “They’d constantly go over video in our room, watching winning World Cup runs every night before bed. Eileen has an amazing eye for it.”

“I just wanted Taylor and Mikaela to make perfect turns,” Eileen said. “It’s like looking for the perfect wave.”

The Shiffrins were disciples of the ten-thousand-hours concept; the 2009 Daniel Coyle book “The Talent Code” was scripture. They studied the training methods of the Austrians, Alpine skiing’s priesthood. The Shiffrins wanted to wring as much training as possible out of every minute of the day and every vertical foot of the course. They favored deliberate practice over competition. They considered race days an onerous waste: all the travel, the waiting around, and the emotional stress for two quick runs. They insisted that Shiffrin practice honing her turns even when just skiing from the bottom of the racecourse to the chairlift. Most racers bomb straight down, their nonchalance a badge of honor.

Jeff Shiffrin said, “One of the things I learned from the Austrians is: every turn you make, do it right. Don’t get lazy, don’t goof off. Don’t waste any time. If you do, you’ll be retired from racing by the time you get to ten thousand hours.”

“Here’s the thing,” Mikaela told me one day. “You can’t get ten thousand hours of skiing. You spend so much time on the chairlift. My coach did a calculation of how many hours I’ve been on snow. We’d been overestimating. I think we came up with something like eleven total hours of skiing on snow a year. It’s like seven minutes a day. Still, at the age of twenty-two, I’ve probably had more time on snow than most. I always practice, even on the cat tracks or in those interstitial periods. My dad says, ‘Even when you’re just stopping, be sure to do it right, maintaining a good position, with counter-rotational force.’ These are the kinds of things my dad says, and I’m, like, ‘Shut up.’ But if you say it’s seven minutes a day, then consider that thirty seconds that all the others spend just straight-lining from the bottom of the racecourse to the bottom of the lift: I use that part to work on my turns. I’m getting extra minutes. If I don’t, my mom or my coaches will stop me and say something.”

The psychologist Ellen Winner has identified a prodigy’s essential traits as “a rage to master” and an ability to learn rapidly. Shiffrin had both. “Her attention to detail and focus on the task at hand is like no one I’ve ever met,” her former coach Brandon Dyksterhouse said. Whereas most skiers could handle, say, six training runs, she could sometimes do eighteen, and whereas most skiers saw their performances tail off in the last three or four, along with their ability to get anything useful out of them, Shiffrin got faster with each run, and her focus never wavered.

Shiffrin, incredibly, almost never “skis out” in training. She completes every practice run without missing a gate or losing control. Dyksterhouse recalls that at one point she went fifty practice days in a row without skiing out, and that she beat every skier who practiced with her on each of those runs. This is not a balance beam: every day the snow and the course are different. She also had the capacity to absorb criticism and integrate refinements into her technique. “You have to have the brain to conceptualize technique and apply it to your body,” Shiffrin said. “If you don’t, you should stop right now.” She was, in a word, eminently coachable. This was opportune, because she happened to be very heavily coached—by her mother.

So, here was this rare combination of tiger mom and willing cub. “I didn’t have that relationship with Taylor,” Eileen told me. “He wanted to do the U.S. ski team. But he didn’t want to make the other boys feel bad. I didn’t understand that. It was like he had three heads.” Taylor raced at the University of Denver, an élite program, and completed an M.B.A. there. An also-ran, by some lights.

When Shiffrin, at the age of sixteen, set out on her first full season on the World Cup tour, her mother travelled with her. “That first year, I didn’t know what I was doing,” Eileen told me. “We were deer in the headlights.” Competition aside, the routine was disorienting. The circuit started in the Alps, moved to North America, then returned to Europe—every few days, a new course, a new town. It was a long way from Burke, from Piglet and Pooh Bear. “All the personalities, the ski-team girls,” Eileen said. “We were a little isolated from them. They didn’t want a kid tagging along, and she didn’t want to tag along.” Mikaela, Eileen said, “wasn’t into the party scene. She was thinking, How am I going to get my math done and where are the bathrooms? It was stressful for me to watch her go through the stress of that.”

The U.S. ski team’s European base was until recently in Sölden, Austria, where a giant glacier enables racers to train early and late in the season. Eileen got an apartment in the neighboring village of Längenfeld. “I tried to give her distance,” Eileen said. “I needed to not be around.” The team travelled by van, and Eileen trailed it in a rental car. At hotels, Mikaela bunked with a teammate, and Eileen got her own room. But by her third year on tour Mikaela was sleeping with her mother instead. “It was more healthy than rooming with a thirty-year-old racer,” Eileen said.

Ski-team officials didn’t necessarily agree. “We were told it was not good for me to be there,” Eileen said. “They’d been through it before, and it hadn’t worked out.”

The coach for slalom and giant slalom was an old-school Austrian named Roland Pfeifer. “Luckily, he was O.K. and open to my mom being around, but he wasn’t so O.K. with it that he wanted her to be coaching me,” Mikaela said. “Eventually, as time went on, he got more and more sensitive to her being one of my coaches. I never would’ve called her a coach when I was working with him.” She went on, “After the last Olympics, my skiing started to fall off, and he got really aggressive about it. It ended up being a pretty nasty split.” Pfeifer was reassigned and then left for the Canadian team.

For the next two years, the women’s coach was Dyksterhouse, who was a kind of emergency call-up from the Vail ski club. Perhaps his relatively humble credentials, or his non-Austrianness, made him a bit more comfortable with Eileen’s omnipresence. Eileen said, “You have to have a couple of coaches who don’t have huge egos, who aren’t territorial and all alpha-male macho about it.”

Still, the situation could get a little intense. “Eileen watches more video than any coach on the planet,” Dyksterhouse said. She texted Mikaela at all hours with observations from her sessions. Dyksterhouse remembers getting a text from Eileen at 5 A.M. the day before the 2015 World Championships, in Vail, saying that she had noticed something. She wanted to wake Mikaela up to show her. Dyksterhouse objected. (“She knows better but she can’t help herself,” one ski-team official told me.) On a few occasions, anticipating that Eileen might pick apart the footage from a day’s session, Dyksterhouse would speed the video up, just enough to elide certain flaws and perhaps shield Mikaela, or, more to the point, Dyksterhouse and his assistant, from an inquisition.

“I got to the point where I didn’t agree with certain things, but how can I argue with the result?” he recalled. “They’ve found an approach that works better than anything in the history of the sport.” He had a behind-the-scenes Web series called “World Cup Diaries,” and on one occasion he posted a side-by-side video comparison he’d worked up of Shiffrin and Frida Hansdotter, one of her top competitors, which he’d annotated, frame by frame, to illustrate Shiffrin’s prowess at gaining speed. Shiffrin told me, “I woke up and had a million texts, from Kilian”—her manager, Kilian Albrecht—“and my mom, saying, like, What was he thinking? Here we are working our tails off, trying to stay one step ahead, and that’s my career, my profession, and why is my coach giving this stuff away?” She made him take it down immediately, but not before some of the European teams had downloaded it for careful study. “I ended up parting ways with him very quickly after that.”

“They went berserk,” Dyksterhouse told me. “They hated, hated, hated that. They’re very secretive.” Nonetheless, he said, it was his decision to leave, owing to his eagerness to work with other racers on the team. Shiffrin mostly trains alone, both because of her demanding schedule and because none of the other women on the team can keep up or handle the workload. (Lindsey Vonn is a team unto herself as well, under the Red Bull flag.)

The coach since then has been Mike Day, but Day recently had back surgery and will miss the first half of the season, so Lackie has taken over. Often the coaches will convey their pointers or critiques to Eileen, who then relays them to Mikaela. When I talked to Tiger Shaw, the head of the whole program, he told me, “The No. 1 thing to recognize is that Eileen is the coach.” As it stands, she has been doing the job, all these years, on her own dime. The ski team doesn’t pay her a salary, and she covers most of her own travel expenses. This might be another reason for her to keep bunking with her daughter. You can take the girl out of New England, but you can’t take New England out of the girl.

Slalom and giant slalom are known as the technical disciplines—tech, for short. The turns are tightest in slalom, wider in G.S. Each turn consists of a pair of poles, several yards apart, and you have to ski through the invisible plane between them—a “gate.” You ski two runs, each lasting less than a minute. The winner is the skier with the lowest combined time. The so-called speed events, downhill and super giant slalom, or super G, have fewer gates, more jumps, greater speed, and higher risk. You get one run.

For decades, slalom courses were set with bamboo poles. You could brush them or whack into them, but it hurt, and they could slow you down or alter your course. So you mostly skied around them, stringing together elegant “S”s. In the eighties, bamboo was replaced by plastic breakaway poles, with a hinge at the base of each, so that you could knock it out of your way; it flopped to the snow and snapped back into place after you’d passed. As a result, skiers started pursuing straighter lines, thrashing through the hinged poles in the manner of an explorer cutting through a thicket with a machete. The progress downhill became more abrupt and violent. Racers began to wear body armor, helmets, and face guards, and to use shorter and shorter skis, the better to whip their feet around the gates. To my eyes, the motocross getups and the herky-jerky descents leached much of the beauty and grace from the sport.

Soon, the tech events were ruled by obscure specialists with names I couldn’t retain and an appeal I couldn’t see. The downhillers, the speed demons who risked life and limb on the classic sheer courses of the Alps, like the Streif, in Kitzbühel, and the Lauberhorn, in Wengen, carried on the sport’s swashbuckling spirit. Even if their best runs seemed reckless and a little haywire, the elegance and power of a well-carved turn, at that speed and in that context, is magisterial. No shin pad can mitigate the pain and misery of cartwheeling into the safety netting at eighty miles an hour.

Still, invincibility is irresistible. A couple of years ago, as Shiffrin’s pursuit of the perfect turn reached a new level, she drew me in. In the fall of 2015, the World Cup season commenced in Aspen. In the opening race, a giant slalom, Shiffrin, carrying a lead into the final pitch, wiped out—uncharacteristically—three gates short of the finish. The next day, she showed up for the slalom in an angry mood. She’d won four in a row to end the previous season. After the first run, she held a lead of nearly a second and a half over the next-fastest racer, a Slovakian named Viktoria Velez Zuzulová. As the leader, Shiffrin was the last out of a field of thirty to ski a second run (forty others had either crashed or failed to qualify), and was thus facing a degraded snow surface. She wore a tight white bodysuit and a stars-and-stripes helmet—a touch of Evel Knievel. The north-facing slope, in full shadow, was a crepuscular blue, out of which the fluorescent yellow trim of her shin and knuckle guards popped like the chest feathers of a chat bird. Banner ads for Milka chocolate (the venue may have been Stateside, but the main television audience was still overseas) lined the run, along with the dim silhouettes of course workers, many of them wearing crampons to maintain their footing on the icy pitch. (It never looks as steep on TV.) Often, Shiffrin’s first few turns are careful, as she establishes a tempo, but on this occasion, despite her almost impregnable lead, she came out “blasting,” as the TV commentator said, so that, by the time she hit the eighteenth gate (out of sixty), the speed and some cruddy snow seemed to cause her to stumble. But she recovered her form—metronomic tempo, skis parallel, body crouched, “knees to skis and hands in front,” as the family mantra goes—and took on the meat of the course with calm determination, to the extent that calmness can be attributed to a woman punching aside heavy, rubbery poles at a rate of more than one a second, while pogoing from side to side in flat light down a wall of rutted ice. Her style was “quiet,” in the argot, the upper body still, skis biting, tip to tail, with hardly a chatter. (Watching the race again recently, on YouTube, I thought of her in high summer, sliding side to side in her socks, holding a medicine ball.) She knocked away the second-to-last gate with both arms, so that for a moment they were raised as though in triumph, and then she ducked across the finish line, swooped into a big turn to check her speed, and finally, snowplowing (pizza!), looked up at the scoreboard. She seemed almost disappointed. She’d won by 3.07 seconds, the largest margin of victory ever in a World Cup slalom race, breaking a record that had stood for forty-seven years.

The following day, there was another slalom race (the second of the season’s nine), and she won again, by 2.65 seconds, the amount of time that separated the second-place finisher from the twenty-third. She said that she’d imagined she was being chased downhill by a bear.

A few days later, at Lake Louise, in Alberta, Canada, Shiffrin entered a super-G race. She came in fifteenth. The winner was Lindsey Vonn. Shiffrin is the best technical skier of her generation, but she aspires to the élite in speed. Some of the American stars, like Vonn and Bode Miller, started out as tech specialists, and then, as they got bigger and stronger and perhaps more courageous and ambitious, began to master the dangers and the demands of the downhill. It’s all skiing, but slalom is Jack-be-nimble while downhill is Jack-be-nuts. One is fast-twitch, the other is barn-on-your-back. The speed and the tech events take place in different locations at different times, with different practice and pre-race regimens. Training for both means training less for each. It may be that interdisciplinary speed is a zero-sum game—that the faster you get in the downhill the slower you go in slalom. This has been true, more or less, of Miller and Vonn, and might well be true of Shiffrin, although she doesn’t have the high tolerance for risk that the others do, and that the speed events seem to require. She and her team wrestle with the problem of giving up a bird in hand to go after one in the bush. “I’m still sort of a risky investment there,” she told me.

Two years ago, the Shiffrins tried to send Mikaela out on tour on her own. “I had decided that that would be the year,” Eileen said. This was after Mikaela’s dominating performance at Aspen. Shiffrin travelled to Sweden without her mother. On the morning of a race, Mikaela crashed and injured her knee, and missed the next couple of months of competition.

“I’m not superstitious, not saying my not being there is why she got hurt, but maybe it was something subconscious,” Eileen said. “Maybe she didn’t approach the day the way she might have. I might have said, ‘Be careful.’ ”

According to Eileen, Mikaela called her and said, “I’m not ready for you to be gone. Clearly, I’m not ready to do this on my own.” Mikaela told me, “I can’t really picture a time when she won’t be on tour with me. Mom has always been my best friend. But, yes, eventually she might get sick of it.”

Bug Pech, when she and Shiffrin were sixteen, promised Shiffrin that she’d watch every race of hers, and so for years, while she was at Boston College and Shiffrin was in the Alps, she got up at four in the morning to tune in. Shiffrin often FaceTimes with her from the physio table. Pech told me, “It’s sort of weird. She’s travelling with three or four middle-aged men, her mom, and her physio, who’s older, too. It can get lonely. When she needs to vent or is frustrated, I get the call.”

The last time Pech saw Shiffrin was at Killington, last year. “I saw her for, like, three minutes,” Pech said. “My mom and sister started tearing up when we had to say goodbye. My sister joked that Mikaela and I have a Romeo-and-Juliet romance.”

This past summer, Mikaela started dating a French giant-slalom skier named Mathieu Faivre. “I don’t know if this is a smart thing to do long distance,” she told Pech.

Pech told her, “For you, everything is long distance.” As she explained to me, “She’s got to have something that’s normal, even if it’s not normal.”

It was her mother who first alerted me to Faivre. “I’m sure you’ve heard, she has a boyfriend in France,” Eileen said. When I mentioned it to Mikaela in a text, she replied with a facepalm emoji: “Oh boy. Hahaha no big deal. He’s a cutie.” Shiffrin made time to visit Faivre in France, and in the fall he went to see her in Vail. He stayed in a hotel. When Shiffrin is home, which isn’t often, she lives with her parents, in the nearby town of Avon. She still doesn’t have a place of her own. (She has earned millions of dollars, in prize money and endorsements. Her father watches over it, with the help of a financial adviser.)

“Some of this for me is about my being able to let her go,” Eileen told me. “My presence is its own burden.”

She went on, “I have my own interests. I like to work out. I like to run. I want to take a nursing refresher course. When Mikaela was at Burke, I was finally getting my career going again, but once she started travelling, what with Jeff the main breadwinner, it was ‘You’re the one to go.’ I don’t regret it. I love spending time with Mikaela. It’s been a privilege for me to do this. But my entire life has been this.”

This will be Mikaela’s seventh year on the tour, and her second trip to the Olympics, where, at least in the American marketplace, reputations and fortunes can be made. She is not oblivious. Talking to people around the ski-team scene, one can find it hard to suss out which of the Shiffrins—if either—might be the one chafing under the current arrangement, or to predict how long it might last. People are watching, with interest.

In October, Mikaela and Eileen left for Austria. Mikaela trained for three days on the Mölltal Glacier, for a week in Sölden, and then for a few days in the Val Senales, in South Tirol, while the F.I.S. prepared the course at Sölden for the traditional season-opening giant slalom there. The day before the race, the International Association of Ski Journalists awarded Shiffrin the Skieur d’Or trophy, as racer of the year. She is the third American, after Miller and Vonn, ever to win it. (Though Shiffrin has not yet become a marketing juggernaut like Vonn, the association called her “a pleasant interlocutor for ski reporters.”) At the bib-drawing ceremony the night before, the announcer, alluding to Shiffrin’s boyfriend, had said to her, onstage, “I hear you learned some French last summer.” Shiffrin, blushing, ventured a pronunciation of “croissant.” Eileen, standing with some ski-team officials, wondered aloud if she’d got it right. The next day, Mikaela, in second place after the first run, hit a rutted, shadowy patch of snow on the steep pitch near the top of her second run, nearly blew out of the course, recovered, and finished a disappointing fifth.

Two weeks later, at the inaugural slalom of the season, at Levi, in Finland, Shiffrin, taking a lead into the second run, again failed to close, losing by a tenth of a second to a Slovakian, Petra Vlhová, of whom Eileen had recently said, “Petra skis like Mikaela more than Mikaela skis like Mikaela.” Was the gap between Mikaela and the field shrinking? Was there something amiss in her form? Was it the gear, the tactics, the training, the chemistry among the coaches, some new warp in her mental makeup? Or was it just the any-given-Sunday principle? A roll of the dice, a bounce of the ball. Second place wasn’t exactly disaster—the top American finisher in the men’s slalom, the next day, placed twenty-third. Still, to the extent that invincibility is a kind of spell, one can never guess when and under what conditions it might break. ♦

An earlier version of this article misstated the year that Joss Christensen won the Olympic gold medal in slopestyle skiing.

This article appears in the print edition of the November 27, 2017, issue, with the headline “Confidence Game.”